This invention relates to tape tensioning apparatus and particularly to such apparatus providing different tensions for different modes of transport of the tape.
In the magnetic tape transport art, it is of great importance to maintain the tape tension at a predetermined value during the play and record modes in order to stabilize the actual speed of the tape across the heads. A similar but slightly less rigorous requirement obtains during the fast-forward and fast-rewind modes in order to prevent slack and throwing of the tap or breaking thereof.
To this end, it is common practice to use spring-loaded tension arms engaging the tape segment between tape moving and anchoring means, such as the capstan and supply reel, for play and record modes; or between the two reels, for fast forward or rewind modes. The transport control and servo system determine the length of tape to be maintained between the anchoring means, and the tension arm senses the actual length in accordance with its own rotational displacement, as the tape segment length changes, and signals this information to the control servo system; the system continuously regulates the tape segment length by operating the tape moving and anchoring means until the desired length is achieved. The tension arm thus has a different position for each mode of operation, and as the arm moves from one of these positions to another, a different spring, or set of springs, is brought into play to establish the tension level desired for the corresponding mode.
In such prior art apparatus, however, the spring force is always increased from, or decreased to, a condition of zero distortion of the spring, so that a substantially uniform play-record tension over a broad range of arm positions is impossible to achieve and this all the more so, as the desired fast forward and rewind tension level values depart from the "play-record" tension level values; and widely different levels for the various modes are in fact desirable, for the transport can be designed to operate more effectively when the mode tension levels are not interdependent and do not restrict one another.
Another problem with the prior art is that there is always substantial frictional shearing motion between various pairs of the tension force transmitting elements, and the friction forces involved must be overcome before the apparatus can respond to changes in the conditions or mode commands; in other words, the response sensitivity or resolution of the apparatus is decreased.
Accordingly, it is an object of the present invention to provide discretely different tension levels for different modes of operation of a tape transport, and particularly to provide a substantially uniform tension value in at least one of these mode levels.
It is another object of the invention to substantially eliminate frictional shearing motion between force transmitting elements of a tape transport tape tensioning apparatus.